Portable x-ray images are used to aid in assessing pathological changes and/or tube/line placement in critically ill patients in the U.S. Over 50% of portable examinations are performed in Critical Care Units (Intensive Care and Coronary Care). The remaining portable exams are performed on the medical or surgical floors or in the Emergency Room. Most patients in a Critical Care Unit have an x-ray procedure at least once per day. The primary portable exam type is AP (anterior-posterior) chest (80% of portable procedures) followed by abdomen and bone. The portable chest radiography market is expected to grow 20% in the United States over the next 5 years.
The technologist's problems in portable radiography are well known: maneuverability of the portable x-ray generator, carrying a large number of cassettes, x-ray tube positioning and determination of proper technique. The variability in positioning the x-ray tube results in different techniques between exams. This sometimes results in over or underexposure so that the radiologist requires an exam to be repeated. The average repeat rate is on the order of 5% to 10%.
The films that are generated while the patient is in a Critical Care Unit are kept in either the radiology department or in the unit. Typically, the most recent films are put on an alternator for easy access and review. Consultation about the procedure occurs where the films are located, requiring either the radiologist or the clinician to go to the films. At some institutions, a double film protocol is used in order to give both the radiologist and clinician easier access to the image.
As radiologists read portable exams, the most current film is compared to previous films to assess changes in the patient's condition. The variability in exposure with current film/screen combinations adds to the difficulty in the assessment of changes that are due to illness.
The clinicians in the Critical Care area often need immediate access to the portable films in order to check proper tube placement. They often "borrow" the film from the radiology department before the radiologist has a chance to read it. Sometimes these films are not returned and a report is not generated; thus the hospital has lost revenue for that exam.
As the population grows older, more people will be hospitalized and require surgery and critical care. Thus the number of portable examinations will increase; the need for better quality and faster portables will increase and hospitals will be in a position to justify the allocation of funds for new systems and additional generators specifically for portable procedures.
In the decades after the end of World War II, there were significant advances in phosphor materials. These advances made high speed electronic imaging possible. Research at Eastman Kodak Company, Rochester, N.Y., led to the first demonstration of a scanned storage phosphor radiographic system. This system was originally patented in 1975 and reissued as U.S. Pat. No. Reissue 31,847, reissued Mar. 12, 1985, to Luckey. In the storage phosphor system disclosed a storage phosphor is exposed to an x-ray image of an object, such as the body part of a patient, to record a latent x-ray image in the storage phosphor. The latent x-ray image is read out by stimulating the storage phosphor with relatively long wavelength stimulating radiation such as red or infrared light produced by a helium neon gas laser or diode laser. Upon stimulation, the storage phosphor releases emitted radiation of an intermediate wavelength, such as blue light, in proportion to the quantity of x-rays that were received. To produce a signal useful in electronic image processing the storage phosphor is scanned in a raster pattern by a laser beam deflected by an oscillating or rotating scanning mirror or hologon. The emitted radiation from the storage phosphor is reflected by a mirror light collector and detected by a photodetector such as a photomultiplier to produce an electronic x-ray image signal. Typically the storage phosphor is translated in a page scan direction past the laser beam which is repeatedly deflected in a line scan direction perpendicular to the page scan motion of the storage phosphor to form a scanning raster pattern of a matrix of pixels.
There is a problem in the prior art of film/screen radiology in providing multiple images with one exposure. Typically, where a radiologist wishes to see multiple levels of edge enhancement or the same edge enhancement with different tonescales, multiple x-ray exposures had to be taken. This is costly, time consuming and unnecessarily exposes the patient to undesirable x-ray exposure. A further problem is presented when multiple versions of an x-ray image signal are created if a destination for the images can not accept all of the images. For example, due to magnetic storage limitations at a workstation, it may be desirable to route only one version there. A laser printer, on the other hand, can reproduce multiple versions of the same exposure on a single film, so it is desirable to route all the versions to the printer.